Stable aqueous solutions comprising titanium and zinc and process therewith

ABSTRACT

A composition that can be used as catalyst in esterification, transesterification or polycondensation is disclosed, which comprises a stable solution comprising (a) titanium in the form of a titanium α-hydroxycarboxylic acid or its salt, (b) a C 1 -C 6  carboxylic acid, and (c) zinc in the form of a water-soluble zinc salt, and (d) water. Also disclosed is an esterification, transesterification or polycondensation process, which comprises contacting, in the presence of the solution composition, an organic acid or its ester or its salt with an alcohol, optionally in the presence of a phosphorus compound, an organic or inorganic toning agent such as cobalt acetate, or combinations thereof. The process can also comprise combining aqueous solutions of a titanium α-hydroxycarboxylic acid or its salt and a zinc salt in an alcohol to produce an alcohol solution contacting the alcohol solution with a mixture comprising organic acid or its ester or its salt and a second alcohol, or comprise combining an aqueous solutions of a titanium α-hydroxycarboxylic acid or its salt and aqueous solution of a zinc salt with the mixture.

FIELD OF THE INVENTION

[0001] This invention relates to a catalyst composition comprising astable aqueous solution of organic titanium and zinc complexes and to aprocess for using the composition in, for example, esterification,transesterification, or polymerization of a carbonyl compound.

BACKGROUND OF THE INVENTION

[0002] Polyesters such as, for example, polyethylene terephthalate,polytrimethylene terephthalate and polybutylene terephthalate, generallyreferred to as “polyalkylene terephthalates”, are a class of importantindustrial polymers. They are widely used in thermoplastic fibers,films, and molding applications.

[0003] Polyalkylene terephthalates can be produced bytransesterification of a dialkyl terephthalate ester with a glycolfollowed by polycondensation or by direct esterification of terephthalicacid with the selected glycol followed by polycondensation. A catalystis used to catalyze the esterification, transesterification and/orpolycondensation.

[0004] Antimony, in the form of a glycol solution of antimony oxide,frequently is used as catalyst in the transesterification oresterification process. However, antimony forms insoluble antimonycomplexes that plug fiber spinnerets and leads in fiber spinning tofrequent shutdowns to wipe spinnerets clean of precipitated antimonycompounds. The antimony-based catalysts are also coming under increasedenvironmental pressure and regulatory control, especially in foodcontact applications.

[0005] Organic titanates, such as tetraisopropyl and tetra n-butyltitanates, are known to be effective polycondensation catalysts forproducing polyalkylene terephthalates in general, and frequently are thecatalyst of choice. However, these catalysts tend to hydrolyze oncontact with water, forming glycol-insoluble oligomeric species whichlose catalytic activity. These organic titanates also generate asignificant amount of yellow discoloration when used aspolyesterification catalysts. Additionally, many organic titanatecatalysts are also substantially insoluble in a polymerization mixturethereby creating non-uniform distribution of catalyst in the mixture.

[0006] U.S. Pat. No. 3,404,121 and U.S. Pat. No. 5,340,907 discloseusing a combination of zinc acetate and tetraisopropyl titanate ascatalysts. When metal salts such as zinc acetate are added to thereaction mass as a solid, it is difficult to control the feed rateuniformly, resulting in variation of the polymerization conditions. Whenadded as a glycol solution, the solubility is quite low and the metalmay precipitate over time. The use of a water solution is not compatiblewith the use of tetraisopropyl titanate because of hydrolysis. Also,water-compatible titanates, when used as polyesterification catalysts,generate significant yellow discoloration in the resultant polymer. See,for example, EP 812818 and WO 99/28033. There is, therefore, a need fora catalyst system that is compatible with water, has good catalyticactivity, and produces a polymer with reduced color.

[0007] Additionally, many solutions of a titanium α-hydroxycarboxylateand a water-soluble zinc salt are not stable, in that they form a cloudysolution or a gel after only a short period of time. This isundesirable, for it may lead to poor control of the catalyst feed to thereaction zone, to an uneven product quality, or to plugging up the downstream spinnerets. Solving this potential problem by adding more wateris undesirable because the added volume makes it difficult to store orship economically. There is also a need for a water-compatible catalystthat has good catalytic activity, produces a polymer with reduced color,is environmentally friendly, does not result in plugging fiberspinnerets, is relatively concentrated, and is stable.

[0008] An advantage of the invention is that a titanium- andzinc-containing catalyst solution can be stabilized for over two weeksunder accelerated storage conditions of 60° C., equivalent to muchlonger storage times at ambient conditions by inclusion of a carboxylicacid. Other advantages of the inventive system will become more apparentas the invention is more fully disclosed herein below.

SUMMARY OF THE INVENTION

[0009] A first embodiment of the invention provides an aqueous catalystcomposition which can be used as an esterification, transesterificationor polycondensation catalyst. The composition comprises a stablesolution comprising (a) titanium in the form of a titaniumα-hydroxycarboxylic acid or its salt, (b) a C₁-C₆ aliphatic carboxylicacid, (c) zinc in the form of a water-soluble zinc salt, and (d) water.

[0010] A second embodiment of the invention provides a process, whichcomprises contacting, in the presence of a solution compositiondisclosed in the first embodiment of the invention, an organic acid orits ester or its salt with an alcohol, optionally in the presence of aphosphorus compound, an organic or inorganic toning agent such as cobaltacetate, or combinations thereof. The process can also comprisecombining aqueous solutions of a titanium α-hydroxycarboxylic acid orits salt and a water-soluble zinc salt in an alcohol and contacting theresulting solution with a mixture comprising organic acid or its esteror its salt and a second alcohol or comprise combining aqueous solutionsof a titanium a-hydroxycarboxylic acid or its salt and aqueous solutionof a zinc salt with the mixture comprising organic acid or its ester orits salt.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The stable aqueous solution comprising organic titanium and zinccompounds can be used as catalyst in esterification,transesterification, polycondensation, or combinations of two or morethereof. If used for polycondensation, it can be added to apolymerization medium before or during the esterification,transesterification, or polycondensation step.

[0012] According to the first embodiment of the invention, astorage-stable catalyst composition is provided, which comprises asolution comprising a titanium α-hydroxycarboxylic acid or salt, a C₁-C₆aliphatic carboxylic acid, a water-soluble zinc salt and water. By“stable”, it is meant that the solution is capable of remaining insubstantial solution and no visible cloud, gel or precipitate appearsunder accelerated storage conditions for at least 2, preferably at least3, and most preferably at least 4 weeks at 25 to about 60° C. underabout atmospheric pressure. The term “substantial” refers to more thantrivial. The term “stable” is also exchangeable with “storage-stable” inthis disclosure.

[0013] Titanium α-hydroxycarboxylic acid can be prepared by reacting atitanium orthoester with an α-hydroxycarboxylic acid. The titaniumorthoester is typically expressed by the general formula Ti(OR)₄ whereeach R is individually selected from an alkyl, cycloalkyl, alkaryl,hydrocarbyl radical containing from 1 to about 30, preferably 2 to about18, and most preferably 2 to 12 carbon atoms per radical and each R canbe the same or different. Examples of commercially available organictitanium compounds include, but are not limited to, TYZOR® TPT andTYZOR® TBT, (tetra isopropyl titanate and tetra n-butyl titanate,respectively), available from E. I. du Pont de Nemours and Company,Wilmington, Del., USA.

[0014] In reaction of a titanium orthoester with an α-hydroxycarboxylicacid, the α-hydroxycarboxylic acid replaces two of the R groups in thetitanium orthoester. Suitable α-hydroxycarboxylic acids include anycarboxylic acid of 1 to 6 carbon atoms comprising carbon, hydrogen andoxygen atoms, and having a hydroxy group in the α-position. Examples ofsuitable α-hydroxycarboxylic acids include, but are not limited to,citric acid, lactic acid, malic acid, tartaric acid, glycolic acid,glyceric acid, α-hydroxybutyric acid, a-hydroxypropionic acid, andcombinations of two or more thereof. The α-hydroxycarboxylic acids arewell known in the art and are disclosed for example in U.S. Pat. No.2,870,181. The reaction can be followed by neutralization with a basesuch as ammonia or an alkali metal, or by reaction with a quaternaryammonium group. The preferred titanium α-hydroxycarboxylate salt istitanium bis-ammonium lactate, commercially available as TYZOR® LA (in asolution form containing 8.2 weight % titanium) from DuPont, Wilmington,Del.

[0015] The composition also includes a water-soluble zinc salt. The term“water-soluble” means that it is soluble in more than a trivial amount.Examples of suitable zinc salts include, but are not limited to, zincacetate, zinc chloride, zinc nitrate, zinc sulfate, and combinations oftwo or more thereof. The preferred zinc salt is zinc acetate.

[0016] The C₁-C₆ aliphatic carboxylic acid useful for producing thesolution can be any carboxylic acid that can produce a stable solutionof the invention. It can be the same α-hydroxycarboxylic acid as thosedisclosed above for producing the titanium α-hydroxycarboxylic acid orsalt. Examples of suitable C₁-C₆ aliphatic carboxylic acids include, butare not limited to, formic acid, acetic acid, propionic acid, butyricacid, pentanoic acid, hexanoic acid, citric acid, lactic acid, malicacid, tartaric acid, glycolic acid, glyceric acid, α-hydroxybutyricacid, α-hydroxypropionic acid, and combinations of two or more thereof.The preferred C₁-C₆ aliphatic carboxylic acid is lactic acid.

[0017] The inventive solution can contain about 0.1 to about 10,preferably about 0.5 to about 10, and most preferably about 0.5 to about2.5 weight % titanium in the form of a titanium α-hydroxycarboxylic acidor its salt, or about 5 to about 30 weight % expressed as commercialtitanium bis-ammonium lactate solution (TYZOR® LA). The inventionsolution can contain about 0.1 to about 30, preferably about 0.5 toabout 30, and most preferably 0.5-20 weight % zinc in the form of awater-soluble zinc salt. The inventive solution can contain 0.05 toabout 10, preferably about 0.1 to about 10, and most preferably 0.1 toabout 5 weight % of a C₁-C₆ aliphatic carboxylic acid. Water generallycan make up the rest of the composition. An example of a preferredsolution can contain about 5-30 weight % titanium bis-ammonium lactatesolution (8.2 weight % titanium), about 1-5 weight % lactic acid, andabout 20-30 weight % zinc acetate, dissolved in water.

[0018] The inventive solution can include other ingredients, such as aphosphorus compound to improve whiteness, or a cobalt compound to act asa color toner or co-catalyst, providing that they do not adverselyaffect the stability of the solution. For example, the storage-stablesolution can contain about 0 to about 15 weight % phosphorus in the formof a water-soluble phosphorus compound, providing the molar ratio of(titanium plus zinc) to phosphorus is greater than about 1.5. Otheringredients such as cobalt can be present in about the sameconcentration as phosphorus.

[0019] The individual components can be combined in any order and thecatalyst composition can be produced by any means known to one skilledin the art. Generally, the mixture can be stirred at a temperature inthe range of from about 0° C. to about 100° C., preferably about 20° C.to about 50° C.

[0020] According to the second embodiment of the invention, a processthat can be used in, for example, the production of an ester orpolyester is provided. The process comprises contacting, in the presenceof a catalyst composition, an organic acid with an alcohol. The catalystcomposition can be the same as that disclosed above.

[0021] A preferred process for producing an ester or polyestercomprises, consists essentially of, or consists of contacting a reactionmedium with a composition disclosed above in the first embodiment of theinvention. The reaction medium can comprise, consist essentially of, orconsist of an alcohol and either (1) an organic acid, a salt thereof, anester thereof, or combinations thereof or (2) an oligomer having repeatunits derived from an organic acid or ester.

[0022] The organic acid or ester thereof can have the formula of R¹COOR¹in which each R¹ independently can be (1) hydrogen, (2) hydrocarboxylradical having a carboxylic acid group at the terminus, or (3)hydrocarbyl radical in which each radical has 1 to about 30, preferablyabout 3 to about 15 carbon atoms per radical which can be alkyl,alkenyl, aryl, alkaryl, aralkyl radical, or combinations of two or morethereof. The presently preferred organic acid is an organic acid havingthe formula of HO₂CACO₂H in which A is an alkylene group, an arylenegroup, alkenylene group, or (4) combinations of two or more thereof.Each A has about 2 to about 30, preferably about 3 to about 25, morepreferably about 4 to about 20, and most preferably 4 to 15 carbon atomsper group. Examples of suitable organic acids include, but are notlimited to, terephthalic acid, isophthalic acid, napthalic acid,succinic acid, adipic acid, phthalic acid, glutaric acid, acrylic acid,oxalic acid, benzoic acid, maleic acid, propenoic acid, and combinationsof two or more thereof. The presently preferred organic diacid isterephthalic acid because the polyesters produced therefrom have a widerange of industrial applications. Examples of suitable esters include,but are not limited to, dimethyl adipate, dimethyl phthalate, dimethylterephthalate, methyl benzoate, dimethyl glutarate, and combinations oftwo or more thereof.

[0023] Examples of carboxylic acid metal salts or esters thereofincludes a 5-sulfo isophthalate metal salt and its ester having theformula of (R²O₂C)₂ArS(O)₂OM in which each R² can be the same ordifferent and is hydrogen or an alkyl group containing 1 to about 6,preferably 2, carbon atoms. Ar is a phenylene group. M can be an alkalimetal ion such as sodium. An example of the ester is bis-glycolate esterof 5-sulfo isophthalate sodium salt.

[0024] Any alcohol that can esterify an acid to produce an ester orpolyester can be used in the present invention. The presently preferredalcohol has the formula of R(OH)_(n), an alkylene glycol of the formula(HO)_(n)A¹(OH)_(n), or combinations thereof in which R is the same asthat disclosed above; n is a number of 1 to about 10, and preferably 1to 5; and A¹ is an alkylene group having 2 to about 10, preferably 2 to7, and most preferably 2 to 4, carbon atoms. Examples of suitablealcohols include, but are not limited to, ethanol, propanol,isopropanol, butanol, ethylene glycol, propylene glycol, isopropyleneglycol, butylene glycol, 1-methyl propylene glycol, pentylene glycol,diethylene glycol, triethylene glycol, 2-ethyl hexanol, and combinationsof two or more thereof. The presently most preferred alcohol is analkylene glycol such as ethylene glycol for the polyester producedtherefrom has a wide range of industrial applications.

[0025] The contacting of an organic acid and alcohol in the presence ofthe catalyst can be carried out by any suitable means. For example, theorganic acid and alcohol can be combined before being contacted with thecatalyst. Also for example, the catalyst can be first dissolved in analcohol by any suitable means such as mechanical mixing or stirringfollowed by combining the solution with (1) a carbonyl compound and (2)an alcohol under a condition sufficient to effect the production of anester or polyester. In the preparation of a polyalkylene terephthalate,it is preferred that the aqueous catalyst solution be dissolved in analkylene glycol and then fed to the reaction mixture.

[0026] The oligomer of an organic acid and alcohol generally has a totalof about 1 to about 100, preferably from about 2 to about 10 repeatunits derived from the carbonyl compound and alcohol.

[0027] Any suitable condition to effect the production of an ester orpolyester can include a temperature in the range of from about 150° C.to about 500° C., preferably about 200° C. to about 400° C., and mostpreferably 250° C. to 300° C. under a pressure in the range of fromabout 0.001 to about 10 atmospheres for a time period of from about 0.2to about 20, preferably about 0.3 to about 15, and most preferably 0.5to 10 hours.

[0028] The molar ratio of the alcohol to organic acid can be any ratioso long as the ratio can effect the production of an ester or polyester.Generally, the ratio can be in the range of from about 1:1 to about10:1, preferably about 1:1 to about 5:1, and most preferably 1:1 to 4:1.

[0029] The catalyst, expressed as Ti, can be present in the range ofabout 0.0001 to about 30,000 parts per million (ppm) by weight of themedium comprising the organic acid and alcohol, preferably about 0.001to about 1,000 ppm, and most preferably 0.001 to 100 ppm. Otheringredients also can be present to enhance catalyst stability orperformance.

[0030] The catalyst composition can be used in producing esters orpolyesters by using any of the conventional melt or solid statetechniques. The catalyst compositions are compatible with conventionalesterification and transesterification catalysts (e.g., manganese,cobalt, and/or zinc salts) and may be introduced to the productionprocess concurrent with, or following, introduction of theesterification catalyst. The catalyst compositions also have been foundto be effective in promoting the esterification reaction, and may beused as a substitute for some or all of the esterification catalyst.

[0031] The second embodiment of the invention also provides anantimony-free process for the preparation of polyalkyleneterephthalates, which comprises combining (1) aqueous solution of atitanium α-hydroxycarboxylic acid or its salt and (2) aqueous solutionof a zinc salt with an alcohol, such as alkylene glycol, to produce aglycol solution and contacting the glycol solution with a mixture ofterephthalic acid or ester and an alkylene glycol monomer under reactionconditions. While the aqueous solution can correspond to that describedin the first embodiment, it is not limited to that composition, i.e., itdoes not have to be a single, storage-stable solution.

[0032] Alternatively, the process for the preparation of polyalkyleneterephthalates can comprise combining (a) aqueous solution of a titaniumα-hydroxycarboxylic acid or its salt in an alcohol and (b) aqueoussolution of a zinc salt in an alcohol, such as alkylene glycol, toproduce a glycol solution and contacting the glycol solutions with amixture comprising an organic acid disclosed above such as terephthalicacid or ester thereof and a second alkylene glycol under esterification,transesterification, or polycondensation conditions. Furtheralternatively, solutions (a) and (b) can be separately combined with amixture comprising an organic acid or ester and an alkylene glycolmonomer under esterification, transesterification, or polycondensationconditions. The definition of titanium, α-hydroxycarboxylic acid, zincsalt, and alcohol and quantities thereof can be the same as thosedisclosed above. Optionally, various stabilizing agents, color toners,co-catalysts or other ingredients can be included in the process, eitherseparately or as part of the above aqueous solutions.

[0033] The invention process can also use a soluble cobalt compound suchas cobalt acetate to aid the catalysis and improve the color of thefinal polymer by acting as a toner. The amount used is preferably fromzero up to about equal weight of titanium used. It can conveniently beadded as part of the inventive catalyst solution providing the amountadded does not interfere with solution stability.

[0034] The invention process can also use a phosphorus compound toimprove the color of the final polymer. While any of the many knownphosphorus color inhibitors for preparation of polyalkyleneterephthalates can be used, phosphoric acid is preferred for its readyavailability. The phosphoric acid can be added separately, or as part ofthe aqueous solution. The amount of phosphorus compound added may be upto about 15 weight % phosphorus relative to the solution, providing itdoes not interfere with solution stability.

[0035] Phosphorus acts to reduce catalyst effectiveness. Preferably itis added after the esterification or transesterification step iscompleted. For example, when using terephthalic acid and ethylene glycolto make polyethylene terephthalate by the esterification route, acatalyst is typically only required for the polycondensation step, andthe phosphorus compound can be part of the aqueous catalyst solution forthe polycondensation. When using dimethyl terephthalate and ethyleneglycol to make polyethylene terephthalate by the transesterificationroute, manganese compounds are typically the transesterificationcatalyst of choice. The use of manganese may cause formation of someundesirable color. The addition of a phosphorus compound can reduce thiscolor problem, and can be added as part of the inventive catalystsolution for the polycondensation step.

[0036] Generally, the preferred molar ratio can be 2≦Zn/Ti≦30 and, ifphosphorus and cobalt are used, 1≦(Ti+Zn+Co)/P≦20.

[0037] A process of particular commercial importance is the productionof polyethylene terephthalate. This is typically carried out by one oftwo routes: the transesterification of dimethyl terephthalate (DMT) withethylene glycol followed by polycondensation, and the esterification ofterephthalic acid (TPA) with ethylene glycol followed bypolycondensation.

[0038] In DMT-based technology, manganese is preferably used astransesterification catalyst in the amount of about 80 to 160 ppm,preferably about 100 to about 120 ppm based on the total quantity ofterephthalic acid. When transesterification is complete a phosphoruscompound, about 0.1 to about 100 ppm P based on the total quantity ofterephthalic acid can be added to deactivate the manganese. Thenantimony (about 200 ppm based on the total quantity of terephthalicacid) or titanium (about 20 ppm based on the total quantity ofterephthalic acid) can be used for the polycondensation step.

[0039] The inventive aqueous catalyst composition can be used in theDMT-based process in several ways. It can be added in thetransesterification step to substitute for all or part of the manganeseto obtain a faster transesterification. Phosphorus can be added toeliminate any manganese used. The inventive catalyst solution can alsobe used in the polycondensation step to eliminate the use of antimony orto reduce the amount of titanium and its related color problems. The useof zinc permits the amount of titanium to be reduced by about 50%. Ifnecessary to improve the color, about 0.1 to about 100 ppm of cobalt canbe added to act as a color toner.

[0040] The inventive catalyst solution can also be used in the TPA-basedprocess. It can be added prior to esterification if there is a need tospeed up this step. Any phosphorus needed can be added afteresterification. Alternatively, the inventive catalyst solution can beadded after esterification to the resulting oligomer. As with theDMT-based process, it can be used in the polycondensation step toeliminate the use of antimony or to reduce the amount of titanium andits related color problems. If necessary to improve the color, about 0.1to about 100 ppm of cobalt can be added as toner.

[0041] The following Examples are provided to further illustrate thepresent invention and are not to be construed as to unduly limit thescope of the invention. All TYZOR® products noted in the examples wereobtained from DuPont, Wilmington, Del., USA.

EXAMPLE 1

[0042] The following solutions were prepared by mixing ingredients shownin Table 1, combining ingredients in any order and mixing by manualstirring at room temperature (about 25° C.), with the weight shown ingrams. The solutions were then stored at 60° C. to provide anaccelerated aging test, and periodically examined for signs ofinstability. Results are shown below. TABLE 1 Composition of TestSolutions A to G Compound A B C D E F G 1) TYZOR ® LA 244 244 244 244244 244 244 2) Zinc acetate 537 537 403 403 268 268 403 3) Water 12001200 800 800 538 538 800 4) Lactic Acid 0 43 0 33 0 22 0 5) Acetic Acid0 0 0 0 0 0 25

[0043] The storage stability tests (by visual observation) showed thatSolution A gelled overnight at 60° C., while Solution B containinglactic acid was storage stable at 60° C. for 4 weeks. Similarly SolutionC gelled in 3 days at 60° C., while Solution D containing lactic acidwas storage-stable at 60° C. for 4 weeks. Solution E became cloudy after21 days at 60° C., while Solution F containing lactic acid wasstorage-stable at 60° C. for 4 weeks. Solution G was also storage-stableat 60° C. for 4 weeks.

[0044] The above tests show that a stable aqueous solution can beprepared by mixing a titanium bis-ammonium lactate complex with lacticacid or acetic acid, zinc acetate and water. If the lactic acid oracetic acid is left out, the mixture will gel or cloud up underaccelerated storage conditions (60° C.).

EXAMPLE 2

[0045] This example shows runs using the inventive catalyst and process.

[0046] The process for producing terephthalic acid-based polymer isillustrated as follows. A 1-liter resin kettle was provided with a JiffyMixer agitator rotating at 40 rpm, a thermocouple, condenser andnitrogen sweep. To this kettle was added the catalyst to be tested, 115ml of ethylene glycol, and 400 g of terephthalic acid oligomer preparedabove. The agitator was turned on and the temperature was increased to275° C. over a period of about 2.5 hours. The contents were polymerizedby holding under agitation at 275° C. and a pressure of 120 mm Hg for 20minutes, and at 280° C. and a pressure of 30 mm Hg for an additional 20minutes. The contents were then held under agitation at 285° C. at 1 to2 mm Hg pressure for a time sufficient to reach 15 ounce-inch (0.106Newton-meter) torque as measured by an Electro-Craft Motomatic torquecontroller. The time for this step was recorded as the Finish Time, andvaried with the catalyst used. The polymer melt was then poured into awater bath to solidify the melt, and the resultant solid annealed at150° C. for 12 hours and ground to pass through a 2 mm filter for colormeasurements using the previously described spectrophotometer. Resultscomparing the color as measured spectrophotometrically are given inTable 2 below.

[0047] Color of the resulting polymer was measured in terms of theL-value and b-value, using an instrument such as the SP-78Spectrophotometer. The L-value shows brightness, with the greater thenumerical value showing higher (desirable) brightness. A value of 78 ormore would be considered good. It will vary with additives such ascobalt.

[0048] The b-value shows the degree of yellowness, with a highernumerical value showing a higher (undesirable) degree of yellowness. Forthe laboratory trials, b colors below 7 would be considered a success.Plant values are different because of differences in methods of processcontrol, additives, etc. For plant trials, results within 2 b units ofan antimony standard would be considered a success. Prior art may showdifferent L and b values depending on scale of operation, quality ofoligomer, quality of recycled glycol, additives, air leakage in system,control of process, and other factors. The only consistent way tomeasure results is by direct comparison with an antimony standard or aprior art catalyst under comparable conditions.

[0049] The following solutions were used as catalysts or additives tothe process.

[0050] Catalyst solution A was made by dissolving 224 g titaniumbis-ammonium lactate solution, 22 g lactic acid, and 123 g of zincacetate in 270 gm of water, followed by agitation to dissolve the zincacetate.

[0051] Catalyst solution B was made by dissolving 224 g titanium bisammonium lactate solution, 43 g lactic acid, and 432 g zinc acetate in1035 g of water, followed by agitation to dissolve the zinc acetate.

[0052] Catalyst solution C was made by dissolving 432 g zinc acetate in1035 g of water, followed by agitation to dissolve the zinc acetate.

[0053] Table 2 shows that the use of mixtures of aqueous solutions oforganic complexes of titanium and zinc had high catalytic activity andproduced esters and polyesters with excellent color value compared touse of zinc or titanium separately. TABLE 2 Performance of CatalystCompositions Ex- am- Ti Zn Co P Time L b Foot- ple (ppm) (ppm) (ppm)(ppm) (min) color color note 1C 10 20 10 65 79.39 8.02 2 2E 10 20 10 3580.85 6.14 3 3C 10 20 5 80 77.50 7.16 2 4E 10 20 5 70 79.05 6.30 3 5C 70105 83.07 4.84 6 6C 25 65 77.30 9.12 7 7E 10 70 50 78.89 6.43 4 8C 10 7050 65 78.53 8.97 4 and 5 9E 10 70 10 55 82.46 5.79 4

[0054] Examples 7 and 9 show the synergism of using Ti in combinationwith zinc compared to Ti (example 6) or zinc (example 5) separately.Zinc by itself (example 5) was too slow. Using Ti only (example 6)required a higher Ti concentration (25 ppm vs 10 ppm) to get similaractivity to example 7 and produced a product that had a higher b value(9.12 vs. 6.43). Examples 7 and 9 show that by combining low levels ofTi with zinc, good catalytic activity and product color were obtained.

[0055] Example 9 differed from example 7 in that 58 g of phosphoric acidwas to catalyst solution B. The addition of 10 ppm P to the mixture of10 ppm Ti and 70 ppm Zn decreased reaction rate slightly, but improvedb.

[0056] Example 8 shows the effect of adding a mixture of Ti and zinc(catalyst B) to an oligomer made using 120 ppm manganese and 50 ppm P.The use of manganese in combination with catalyst B gave (resulted in) aproduct having (a) much higher b color (8.97 vs. 6.43).

1. A solution composition comprising, or produced by combining, (a)titanium in the form of a titanium α-hydroxycarboxylic acid or its salt,(b) a C₁-C₆ aliphatic carboxylic acid, (c) zinc in the form of awater-soluble zinc salt, and (d) water.
 2. A composition according toclaim 1 further comprising phosphorus in the form of a water-solublephosphorus compound.
 3. A composition according to claim 2 wherein themolar ratio of (titanium plus zinc) to phosphorus is greater than about1.5.
 4. A composition according to claim 1 further comprising awater-soluble cobalt compound.
 5. A composition according to claim 3further comprising a water-soluble cobalt compound.
 6. A compositionaccording to claim 1 wherein said α-hydroxycarboxylic acid is citricacid, lactic acid, malic acid, tartaric acid, glycolic acid, glycericacid, α-hydroxybutyric acid, α-hydroxypropionic acid, or combinations oftwo or more thereof.
 7. A composition according to claim 6 wherein saidC₁-C₆ aliphatic carboxylic acid is formic acid, acetic acid, propionicacid, butyric acid, pentanoic acid, hexanoic acid, citric acid, lacticacid, malic acid, tartaric acid, glycolic acid, glyceric acid,α-hydroxybutyric acid, α-hydroxypropionic acid, or combinations of twoor more thereof.
 8. A composition according to claim 7 wherein saidtitanium α-hydroxycarboxylic acid or its salt is titanium bis-ammoniumlactate.
 9. A composition according to claim 3 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.10. A composition according to claim 5 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.11. A composition according to claim 1 wherein said C₁-C₆ aliphaticcarboxylic acid is lactic acid.
 12. A composition according to claim 3wherein said C₁-C₆ aliphatic carboxylic acid is lactic acid.
 13. Acomposition according to claim 9 wherein said C₁-C₆ aliphatic carboxylicacid is lactic acid.
 14. A composition according to claim 10 whereinsaid C₁-C₆ aliphatic carboxylic acid is lactic acid.
 15. A compositionaccording to claim 1 wherein said water-soluble zinc salt is zincacetate.
 16. A composition according to claim 11 wherein saidwater-soluble zinc salt is zinc acetate.
 17. A composition according toclaim 12 wherein said water-soluble zinc salt is zinc acetate.
 18. Acomposition according to claim 14 wherein said water-soluble zinc saltis zinc acetate.
 19. A composition according to claim 1 wherein thesolution contains about 5 to about 30 weight % titanium bis-ammoniumlactate, about 1 to about 5 weight % lactic acid, and about 20 to about30 weight % zinc acetate.
 20. A process comprising contacting, in thepresence of a catalyst, (1) an organic acid or its salt or its esterwith (2) an alcohol wherein said catalyst comprises, or is produced bycombining, (a) titanium in the form of a titanium α-hydroxycarboxylicacid or its salt, (b) a C₁-C₆ aliphatic carboxylic acid, (c) zinc in theform of a water-soluble zinc salt, and (d) water.
 21. A processaccording to claim 20 wherein said α-hydroxycarboxylic acid is citricacid, lactic acid, malic acid, tartaric acid, glycolic acid, glycericacid, α-hydroxybutyric acid, α-hydroxypropionic acid, or combinations oftwo or more thereof.
 22. A process according to claim 21 wherein saidC₁-C₆ aliphatic carboxylic acid is formic acid, acetic acid, propionicacid, butyric acid, pentanoic acid, hexanoic acid, citric acid, lacticacid, malic acid, tartaric acid, glycolic acid, glyceric acid,α-hydroxybutyric acid, α-hydroxypropionic acid, or combinations of twoor more thereof.
 23. A process according to claim 22 wherein saidcatalyst further comprises phosphorus in the form of a water-solublephosphorus compound.
 24. A process according to claim 23 wherein themolar ratio of (titanium plus zinc) to phosphorus is greater than about1.5.
 25. A process according to claim 22 further comprising awater-soluble cobalt compound.
 26. A process according to claim 24further comprising a water-soluble cobalt compound.
 27. A processaccording to claim 22 wherein said titanium α-hydroxycarboxylic acid orits salt is titanium bis-ammonium lactate.
 28. A process according toclaim 24 wherein said titanium α-hydroxycarboxylic acid or its salt istitanium bis-ammonium lactate.
 29. A process according to claim 26wherein said titanium α-hydroxycarboxylic acid or its salt is titaniumbis-ammonium lactate.
 30. A process according to claim 22 wherein saidC₁-C₆ aliphatic carboxylic acid is lactic acid.
 31. A process accordingto claim 23 wherein said C₁-C₆ aliphatic carboxylic acid is lactic acid.32. A process according to claim 27 wherein said C₁-C₆ aliphaticcarboxylic acid is lactic acid.
 33. A process according to claim 28wherein said C₁-C₆ aliphatic carboxylic acid is lactic acid.
 34. Aprocess according to claim 22 wherein said water-soluble zinc salt iszinc acetate.
 35. A process according to claim 30 wherein saidwater-soluble zinc salt is zinc acetate.
 36. A process according toclaim 31 wherein said water-soluble zinc salt is zinc acetate.
 37. Aprocess according to claim 33 wherein said water-soluble zinc salt iszinc acetate.
 38. A process according to claim 22 wherein said solutioncomprises or is produced by combining about 5 to about 30 weight %titanium bis-ammonium lactate, about 1 to about 5 weight % lactic acid,and about 20 to about 30 weight % zinc acetate.
 39. A process accordingto claim 38 wherein said organic acid is terephthalic acid, said esteris dimethyl terephthalate, and said alcohol is ethylene glycol.
 40. Aprocess comprising contacting, in the presence of a stable solution, anorganic acid or its salt or its ester with an alcohol wherein saidstable solution comprises or is produced by combining about 5 to about30 weight % titanium bis-ammonium lactate, about 1 to about 5 weight %lactic acid, and about 20 to about 30 weight % zinc acetate, based onthe total weight of said organic acid; said organic acid or its salt orits ester is terephthalic acid or dimethyl terephthalate; and saidalcohol is ethylene glycol.
 41. A process according to claim 40 whereinthe molar ratio of Zn to Ti is in the range of from 2 to
 30. 42. Aprocess according to claim 41 wherein said process is carried out in thepresence of a phosphorus compound.
 43. A process according to claim 42wherein said process is carried out in the presence of a cobalt compoundand the molar ratio of (Ti+Zn+Co)/P is from 1 to 20.